Study: Earthquake clusters are random

Analysis by U.S. Geological Survey concludes clusters random

ALBANY, Calif. |
August 3, 2012

A theory that earthquakes come in clusters because they "communicate" across large distances and trigger each other doesn't hold up, U.S. researchers say.

While the past decade has seen such a cluster of large earthquakes, with massive temblors striking Sumatra, Chile, Haiti and Japan since 2004, a new analysis by U.S. Geological Survey seismologists concludes it could just as well be the result of random chance.

To determine if the quake clusters in the 2000s and a similar one in the 1960s could be attributed to random chance, Tom Parsons and Eric Geist looked at the timing between the world's largest earthquakes -- magnitude 8.3 and above -- at one-year intervals during the past 100 years.

The intervals are similar to what would be expected from a random process, they found.

In other words, the global hazard of large earthquakes remains constant over time, they said in a release from the Seismological Society of America.

Except in the case of local aftershocks, the probability of a new large quake occurring isn't related to past global quakes, they said.

That could be good news after a decade of destruction, they added, since a specific number of quakes that cluster together within a short time is unlikely to be repeated in a similar way over a 100-year span.